F.A.A. to Order Airlines to Inspect 737s for Cracks

The Federal Aviation Administration announced on Monday that it would require extensive inspections of some older-model Boeing 737s for cracks in the planes’ fragile skin that can be caused by pressurization and depressurization of the cabin over tens of thousands of takeoffs and landings.

Three days earlier, undetected cracks widened into a five-foot hole in the roof of a Southwest Airlines flight, forcing the plane, a 737-300, to make an emergency landing at a military base. The F.A.A. announcement applies to 175 aircraft worldwide, including 80 that are based in the United States. Most are operated by Southwest, which started inspections over the weekend and has found three more planes with small cracks.

The airline also canceled 70 flights from its schedule of 3,400 departures on Monday. About 300 flights were canceled on both Saturday and Sunday.

The incident on Friday was at least the third involving metal fatigue in the last few years, and the most terrifying. The others involved another Southwest 737-300 flight in 2009 and an American Airlines Boeing 757 last year.

The recent string of similar problems has baffled safety experts who said the industry assumed it had successfully resolved the problem of metal fatigue after an accident in 1988 involving a 737 jet flown by Aloha Airlines. During the flight, an 18-foot section of the forward cabin ripped open and a flight attendant was blown out of the plane.

Southwest insisted that it had done all the required inspections of its aircraft. But the latest problem focused attention on how the carrier uses its planes on up to 12 flight segments a day. Other airlines, which often fly longer routes, typically have six to eight segments for their planes. The plane involved in the incident on Friday had logged 39,000 takeoffs and landings, a relatively high number for a 15-year-old aircraft.

Photo

A member of the N.T.S.B. investigating the emergency landing of Southwest Airlines Flight 812 cut away a portion of the plane's fuselage on Sunday, in Yuma, Ariz. Credit
Craig Fry/The Yuma Daily Sun, via Associated Press

The F.A.A. directive focused on planes that had accumulated a large number of takeoff and landing cycles. It applies not only to the 737-300 model but also to similar 737-400 and 500 models, a design that dates back to the early 1980s and is known as the 737 Classic series.

“This was a very serious failure,” said William R. Voss, the president and chief executive of the Flight Safety Foundation, an independent nonprofit group. “Is there something wrong with the inspections we’ve been using in the past 20 years, or was there something wrong on the inspection with this one plane?”

Hans J. Weber, owner of Tecop International, an aviation consulting firm in San Diego, said that jetliners could easily survive a small crack in the aluminum skin on the fuselage. But what happened in the Aloha accident and the more recent incidents is that multiple small cracks appeared near rivets in areas where the plane experiences the most stress, causing the skin to peel back. “It’s like it unzips,” Mr. Weber said.

The F.A.A. directive is intended to detect cracks in places where the skins overlap and other structural weaknesses, J. Randolph Babbitt, the F.A.A. administrator, said in a statement. The directive came shortly after Boeing, the manufacturer, said it was also recommending that airlines inspect the areas where the skin covers joints on the older 737 models.

The National Transportation Safety Board, which is conducting an investigation into Friday’s incident, said that it was probably the result of fatigue cracks in these joints. Southwest began flying the plane, which carried 118 passengers, in 1996 and it is among the oldest in its fleet.

Mr. Weber said that after the Aloha accident, metal fatigue was a big issue, and the F.A.A. began to require the airlines to conduct more frequent and intense inspections as planes aged and accumulated more takeoffs and landings.

“Over the last few years, the attitude has been that we solved the fatigue problem,” he said. “But are we seeing what happens when attention wanders to something else, that we slip a little bit in the quality of the work we do? This is just speculation, but this is what I’m worried about.”

Whitney Eichinger, a spokeswoman for Southwest, said the airline was in full compliance with all F.A.A. and Boeing inspection requirements. “We take safety very seriously as do our maintenance folks, which is why our safety record is so solid,” she said.

One expert, John J. Goglia, a former N.T.S.B. member, said that the Flight 812 episode might lead to a change in how airlines look for metal fatigue. “The cracking has been known about for a long time,” he said. “It’s nothing new. What might be new is finding it at this location.”

But Mr. Weber said that even if the exact location was different from earlier incidents, the fact that it occurred in the roof of the plane “was no surprise.” He added, “Everyone knows the highest stress areas are up in the crown.”

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This is not the first time that a Southwest plane has had a crack in flight. In July 2009, another plane developed a skin fatigue problem that caused a small puncture in its fuselage.

And last year, an American Airlines Boeing 757 experienced a sudden decompression after a 1-foot by 2-foot hole opened in its fuselage in the upper crown above the left door. This prompted the F.A.A. to issue a new airworthiness directive requiring repetitive inspections of more than 680 757s operated by airlines in the United States. The latest F.A.A. directive will require initial inspections that use low-voltage electric currents, called Eddy currents, to help inspectors detect cracks in the 300, 400 and 500 series 737s that have accumulated more than 30,000 flight cycles. It will then require “repetitive inspections” at regular intervals. More details are expected Tuesday when the directive is formally released.

Mike Boyd, the chief executive of Boyd Group, an aviation consulting firm, said that while the Southwest episode may seem traumatic, especially to passengers on board, they are, in fact, extremely rare and would not have much impact on how Southwest or other airlines run their operations.

“You can always find cracks on an airplane, but I don’t think this is going to be earth-shattering to anybody,” he said.

Correction: April 5, 2011

An earlier version of this article erroneously identified John J. Goglia as a former chairman of the N.T.S.B.

Joseph Berger and Duff Wilson contributed reporting.

A version of this article appears in print on April 5, 2011, on Page A1 of the New York edition with the headline: More 737 Cracks Found; U.S. Seeks Inspections. Order Reprints|Today's Paper|Subscribe